Chemistry Unit 3

  • Created by: YOIMO
  • Created on: 10-06-17 16:25

C3.1 The periodic table

  • in 1863 Newlands proposed his law of octaves where the 8th element always had similar characteristic. he put the 62 elements in 7 groups but scientists did not accept it as after calcium their properties did not match very well within the groups. he did not include unknown elements
  • in 1869 Mendeleev produced a better table where he left gaps for the undiscovered and he predicted properties for them. he was correct so scientists believed him
  • the reactivity of metals in a group increases going down the group because the outer electron is less strongly attracted to the nucleus as the number of occupied energy shells increases and the atoms get larger
  • reactivity of non-metals decreases going down a group because the attraction of the outer electrons to the nucleus decreases as the number of occupied energy shells increases
  • group 1 elements are alkali metals
  • when the alkali metals react with water they produce the metal hydroxide and hydrogen gas
  • eg sodium + water -> sodium hydroxide + hydrogen
  • transition metals: high bp, high mp, malleable, ductile, good conductors of heat and energy, react only slowly or not at all with oxygen and water, strong, dense, positive ions, compounds are often brightly coloured, catalysts for some chemical reactions
  • halogens are the name of group 7 elements
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C3.2 Water

  • hard water uses more soap to produce a lather and to wash effectively because it contains dissolved compounds such as calcium and magnesium salts
  • calcium and magnesium ions in hard water react with soap producing a precipitate called scum
  • soapless detergents do not react with hard water to form scum
  • temporary hard water can produce a solid scale when it is heated, reducing the efficiency of heating systems and kettles. it contains hydrogencarbonate ions (HCO3-) decompose when heated to produce carbonate ions, water and carbon dioxide. 2HCO3 -> CO3 + H2O + CO2 the carbonate ions react with calcium and magnesium ions in the water to produce precipitates of calcium carbonate and magnesium carbonate that are deposited as scale
  • hard water is good for your teeth bones and reducing heart disease
  • both types of hard water can be softened by adding washing soda or by using an ion-exchange resin which contains sodium and hydrogen ions
  • soft water does not produce scale or scum and it lathers easily
  • safe water has low levels of dissolved salts and microbes
  • water is treated by: sedimentation & filtration to remove solids, disinfection to kill microbes, silver prevents the growth of bacteria
  • chlorine kills microbes but it's poisonous and can produce other toxic compounds
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C3.3 Energy Calculations

  • when fuels and foods react with oxygen the reactions are exothermic
  • we use a calorimeter to measure the amount of energy released when substances burn
  • a simple calorimeter can be used to measure energy changes in solution
  • to make the experiment more accurate we use: a styrofoam cup- insulator, lid- keep heat in and a data logger
  • bond breaking is endothermic
  • bond making is exothermic
  • the minimum energy required for a reaction is called the activation energy
  • bond energy- the energy needed to break a particular chemical bond
  • hydrogen can be burned in combustion engines or can be used in fuel cells to power vehicles
  • disadvantages of hydrogen: supply, storage and safety problems
  • fuels need to match the performance, convenience and costs of petrol and diesel vehicles
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C3.4 Analysis and synthesis part1

  • tests for positive ions:
  • -Flame test- LiC, NaY, KiL, Car, BaG
  • -Sodium hydroxide- ALuminium, CAlcium, MaGnesium ions form white precipitates CAAL MG. White and excess sodium hydroxide solution is added the precipitate of aluminium hydroxide dissolves, CuB, FeG, FeB.  EG. Fe3+  +  3OH-  ->  Fe(OH)3
  • tests for negative ions:
  • -Carbonate ions: Hydrochloric acid- it will produce gases which make it fizz and bubble turning the limewater cloudy.  EG. 2HCl + CaCO3  ->  CaCl2  +  H2O  + CO2
  • -Halide ions: add dilute Nitric acid and silver nitrate solution- CloWn, BriCk, tIDY.   EG.    AgNO3 + NaCl -> AgCL + NaNO3
  • -Sulfate ions: add dilute hydrochloric acid and then barium chloride solution- if a white precipitate forms then sulfate ions are present. EG. BaCl2 + MgSO4 -> BaSO4 + MgCl2
  • a titration is used to measure accurately how much acid and alkali react together completely
  • titrations: pipette measures volume of alkali that is put into a conical flask, indicator is added to the alkali, a burette is filled with acid, the acid is gradually added to the flask, when the indicator changes colour then the end point has been reached, the volume of acid used is the final take away the initial, it is done several times to improve the repeatability
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C3.4 Analysis and synthesis part2

  • titrations calculations: number of moles=mass in grams/relative formula mass
  • concentrations of solutions are measured in g/dm3 or mol/dm3
  • qualitative analysis is the aesthetics eg tests for ions
  • quantitative analyse is the mass change eg titrations, mass or gas spectrometer
  • in a closed system equilibrium is achieved when the rates of the forward and reverse reactions are equal ie equilibrium
  • an increase in pressure on the side with more molecules will decrease the products formed
  • if the forward reaction is endothermic and the temperature increases then the amount of products formed will increase
  • the Haber process makes ammonia for fertilisers and other chemicals
  • nitrogen comes from the air and hydrogen is from natural gas
  • the gases pass over an iron catalyst, 450' and 200ATM as fastest reaction rate & fair yield
  • it is a reversible reaction N2 + 3H2 -><- 2NH3 which is exothermic where they work best in low temp but the iron catalyst becomes ineffective so it takes longer- compromise of 450'
  • some of the ammonia that is produced breaks down into nitrogen and hydrogen and the yield of ammonia is only about 15%
  • the gases that come out of the reactor are cooled so the ammonia condenses. the liquid ammonia is separated from the unreacted gases (they're recycled)
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C3.5 Organic chemistry part1

  • homologous series- a group of related organic compounds that have the same functional group eg the molecules of the homologous series of alcohols all contain the -OH group
  • alcohol -OH  EG. ethanol: molecular formula- C2H6O structural formula- CH3CH2OH
  • carboxylic acid -COOH  EG. ethanoic acid: molecular- C2H4O2 structural- CH3COOH
  • esters -remove H2O EG. ethyl ethanoate: molecular- C4H8O2 Structural- CH3COOC2H5
  • meth x1, eth x2, prop x3, but x4
  • sodium reacts with alcohols to produce hydrogen gas, but the reactions are less vigorous than when sodium reacts with water
  • combustion reaction: ethanol + oxygen -> carbon dioxide + water
  • ethanol can be oxidised to ethanoic acid, either by chemical oxidising agents or by the action of microbes. ethanoic acid is the main acid in vinegar
  • when carboxylic acids are added to carbonates they fizz because they react to produce carbon dioxide and also salt and water are produced
  • carboxylic acids react with alcohols in the presence of an acid catalyst eg ethanol and ethanoic acid react together when mixed with sulfuric acid to produce ethyl ethanoate and water
  • esters are volatile compounds and have distinctive smells so they're used in perfumes and food flavourings
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C3.5 Organic chemistry part2

  • acids that ionise completely in aqueous solutions are known as strong acids
  • acids that ionise completely in aqueous solutions are known as weak acids
  • you can tell that a solution is acidic if it has a pH less than 7 and it fizzes when added to a carbonate
  • testing to see if it's hard water: add soap solution and shake, scum forms & does not lather
  •  (
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